Many of today's portable devices, such as MP3 players, portable DVD players, digital cameras, camcorders, notebook computers, etc., now include video outputs such as composite video, S-video, component video, and analog RGB video with horizontal sync and vertical sync. Such portable devices typically include an output video circuit which receives an input video signal from a digital-to-analog converter (DAC). Generally, the output video circuit includes a low pass filter for filtering the output signal of the DAC, and an amplifier to provide some gain to the filtered signal (e.g., 6 dB). Typically, the output video circuit of these portable devices remain ON (i.e., continues to draw power) even when there is no load connected to the video output.
With portable devices, conservation of battery power is given considerable attention in the design of these devices. A portable device having a longer operating time without requiring a recharge of its internal battery provides a competitive advantage for the device. However, a portable device that maintains its output video circuit powered ON even when there is no load connected to its video output results in a needless waste of battery power.
To address this issue, some prior portable devices include a mechanical sense pin on the output video connector. When a load is connected to the output video connector, the mechanical sense pin is depressed, which is sensed by a microcontroller. In response, the microcontroller turns ON the output video circuit. When the load is subsequently removed, the mechanical sense pin is released, which is also sensed by the microcontroller. In response, the microcontroller turns OFF the output video circuit.
There are several issues with the mechanical sense pin device. First, such connector having a built-in mechanical sense pin is typically expensive, which adds to the cost of manufacturing the portable device. Second, the sense pin being mechanical, is subject to wear and tear and possible damage. Third, generally software is required to control the microprocessor to recognize when the mechanical sense pin has been depressed, and in response, activate the output video circuit; and to recognize when the mechanical sense pin has been released, and in response, de-activate the output video circuit.